Flush tank



FIG. 1 is a perspective view taken from the top, front and right side of a flush tank showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a left side elevational view thereof, the right side being a mirror image of the left side;

FIG. 4 is a front elevational view thereof; and,

FIG. 5 is a rear elevational view thereof. 

The ornamental design for a flush tank, as shown and described. 